Embodiments of the present invention relate to semiconductor memory devices and methods of forming the same, and more particularly, to nonvolatile semiconductor memory devices and methods of forming the same.
Generally, semiconductor memory devices can be classified as volatile memory devices or nonvolatile memory devices. Volatile memory devices lose their stored data when their power supplies are interrupted while nonvolatile memory devices retain their stored data even when their power supplies are interrupted. Flash memory devices, which are nonvolatile memory devices, are highly integrated devices developed by combining advantages of an erasable programmable read only memory (EPROM) capable of programming and erasing data and an electrically erasable programmable read only memory (EEPROM) capable of electrically programming and erasing data.
Flash memory devices may be classified as NOR-type flash memory devices or NAND-type flash memory devices. The NAND-type flash memory device is advantageous in highly integrated devices because a plurality of memory cells are controlled at one time as a string. A NAND-type flash memory device includes ground select lines arranged on one side of a group of word lines and string select lines arranged on the other side of the group of word lines.